The present invention relates to an implosion prevention band fitted to the external surface of a faceplate panel having reduced curvature of an evacuated and sealed cathode-ray-tube (CRT) and in particular, to a tension band wherein the width and corners of the tension band are designed to maximize the compressive forces on the panel face.
A conventional color CRT includes a glass faceplate panel with a sidewall and a funnel sealed to the faceplate sidewall along a planar sealing interface. The CRT is evacuated to a very low pressure causing the tube to deform mechanically with resulting stresses produced by the vacuum and by the atmospheric pressure acting on all surfaces of the CRT. Accordingly, such stresses subjects the tube to the possibility of implosion as a result of an impact to the glass faceplate panel. Such impact to the glass faceplate panel can cause the panel to shatter into many fragments, projecting the glass fragments in random directions with considerable force.
The most common solution to the implosion problem is to use convexly curved faceplate panels with increased glass thickness near the edges of the faceplate panel to resist the stresses described above. In conjunction with the curved faceplate panel, it is also known to use an implosion prevention band consisting of a metal shrink band in hoop tension over, and tightly against, the faceplate sidewalls, so as to exert a radial compressive force to the sidewalls of the faceplate panel. It is also known to fasten metal strips along the straight edges of the sidewall of the curved faceplate panel underneath the metal tension shrink band. The metal strips redistribute the compression load applied by the tension band to the straight edge sides of the sidewall, so that the load is not concentrated at the corners of the faceplate panel. Normally, the shrink band extends over and covers the mold match line of the faceplate panel and the majority of the sidewall.
The curvature of the faceplate panel allows for the vacuum forces within the tube to be distributed through the faceplate panel. However, deformation of the tube also introduces tensile stresses throughout the faceplate panel and sidewalls. The bands are used to apply a compressive force to the sidewalls of the CRT to redistribute some of the faceplate panel forces. The redistribution of the faceplate forces decreases the probability of an implosion of the tube by minimizing tension forces in the sidewalls and corners of the faceplate panel. Implosion prevention bands are also beneficial because they improve the impact resistance of the tube. Glass in compression is stronger than glass which is not in compression. The band causes compression in faceplate areas which otherwise are in tension. Additionally, in the event of an implosion the redistributed stresses cause the imploding glass to be directed toward the back of the cabinet in which the tube is mounted, thereby substantially containing the glass fragments of the imploding tube.
The curved faceplate panels described above require that the mask be curved. However, television tubes having flatter viewing surfaces also employ a relatively flat mask and similarly shaped faceplate panel faces, i.e., viewing surfaces. Unfortunately, the implosion protection techniques that have been used successfully with curved faceplate panel tubes have proven inadequate when used with these CRTs having reduced curvature or completely flat faceplate panels. Flatter faceplate panels under vacuum loads still flex inwardly as a result of the vacuum pressure. However, the lack of curvature in the flatter faceplate panels causes high tensile stresses near the viewing surface of the panel. When prior art implosion protection bands are used on a flatter faceplate panel tube, the bands extend far aft of the viewing surface along the sidewall and tend to deflect the sidewall inwardly thereby increasing the tension on the viewing surface of the faceplate panel. Consequently, the prior art implosion protection bands cannot supply large enough compressive loads upon the faceplate panel. Therefore, the tensile stresses on the faceplate panel are not sufficiently reduced. Moreover, tubes having highly rectangular flat faceplate panels, such as in wide screen televisions using a 16:9 aspect ratio instead of the standard 4:3 aspect ratio of a normal square television, will be subject to additional pressure exerted on the glass along the straight edge of the sidewall with the use of such prior art bands due to the elongated sides of the panel. Consequently, the degree of implosion protection on flat faceplate panels by conventional implosion bands is greatly reduced.
The present invention relates to a shrink band that cooperates with the faceplate panel of the CRT having reduced curvature to help prevent dangerous implosions.
According to the aspect of the present invention, the CRT comprises an evacuated envelope having a mask and corresponding faceplate panel having rounded corners and a sidewalls joined to a funnel. The faceplate panel and sidewalls form an inside blend radius around the inner periphery of the faceplate panel. The band extends along the exterior surface of the sidewall such that the width of the band terminates at or near the inside blend radius of the faceplate panel. The band is under tension to produce radially inwardly directed force components primarily through the corners of the faceplate panel at or near the inside blend radius to produce a high degree of implosion protection for the CRT.